Audio/MIDI Interfaces

OK so I've had my Steinberg MI4 for years now but it's pretty much come to the end of the road as it is now almost completely unsupported and I can only get it to the very basic functions (i.e. MIDI input and audio output).
My set up is: Logic Pro 9, MacBook Pro, 2 x Adam A8X Monitors, Sennheiser HD-25 II, MIDI Keyboard, Sennheiser e815s mic and, currently, the MI4.
What I'm looking for is a USB or Firewire audio interface that will basically allow me to plug my MIDI keyboard in and route it to Logic, allow me to plug the mic in and route that to Logic and output Logic to the monitors - the MI4 allows me to do all this at the moment except for the mic bit (it did on my old Windows setup) but the lag is almost unusable.
Any suggestions? Everything seems to be 200-300, surely there is something that does this job for less?